This invention relates to mixtures (alloys) of polyacrylate resins and siloxane-styrene copolymers for use in fabricating contact lenses. More particularly, this invention concerns mixtures of polymethylmethacrylate (PMMA) and polydimethylsiloxane-.alpha.-methylstyrene block copolymers.
Polymethylmethacrylate and similar polyacrylate resins are frequently utilized to fabricate contact lenses since they offer a combination of exemplary properties including clarity, flexibility, dimensional stability and durability. The oxygen permeability of contact lenses fabricated from these materials, however, often results in corneal edema since ocular tissue satisfies some of its oxygen requirements by direct atmosphereic contact. Consequentially, a significant portion of the population cannot comfortably wear lenses of the polyacrylate class. In all cases, extended wear of such polyacrylate lenses is not recommended.
Although the enhanced permeability of most soft lens systems now on the market may compensate for this deficiency, the preciseness of optics, including the ability to correct for astigmatism, is sacrificed. Also, the dimensional stability of the so-called hydrogels is poor. An excellent paper dealing with oxygen permeability of contact lenses is "Corneal Physiology And Permeable Materials" by Robert B. Mandell which was delivered in New Orleans, La. on Oct. 22, 1981, published by Contact Lens Manufacturers Association. A more recent review of these materials is provided by Refojo, F., "Current Status of Biomaterials in Ophthalmology," Survey of Ophthalmology 26:5, pgs. 257-265 (March-April 1982).
The incorporation of various siloxane containing methacrylate monomers into copolymers has been shown to increase the oxygen permeability of polyacrylate resins. U.S. Pat. Nos. 3,808,178; 4,139,513; 4,139,692; 4,152,508 and 4,153,641 are indicative of this approach. The use of methacrylate silicones for contact lenses is described in "New-Generation Silicones For Medical Devices" by Barry C. Arkles (the applicant herein), Medical Device and Diagnostic Industry, Volume 3, No. 4, April 1981, Canon Communications, Inc.